The paper gives a précis account of studies made at the Rocket Propulsion Establishment of the Ministry of Aviation to determine the relationship between the specific weight and thrust of a liquid bi-propellent rocket engine.

Although the need for a better understanding of basic phenomena is established, the conclusion is reached that, within the selected premises, the minimum specific weight is achieved at a thrust level near 50,000 lb. The difference in specific weight between engines of 200,000 lb. thrust and 50,000 lb. thrust is only about 10 per cent and this is shown to be equivalent to only one per cent in propellent specific impulse. Although small, it is considered significant that a minimum has been established and this fact is used as an argument to justify the use of clusters of engines (generally four) to provide levels of thrust greater than 100,000 lb.